Research On Sensors' Arrangement And Auditory Localization For Acoustic Emission Testing

Offshore platform as the basic facilities for exploiting marine resources is a base for production and activities. It is important to detect cracks in offshore platform timely to prevent the accidents. Acoustic emission technology as a new type of dynamic detecting technology has been widely used in many fields. The study of acoustic emission testing technology of offshore platform is helpful to master offshore platform health in real time. In this paper, the sensors'arrangement and auditory localization for acoustic emission testing of offshore platforms have been studied, and the purpose is to use few sensors to achieve the global testing and to provide the basis for safety evaluation and health diagnosis of offshore platform.In this paper, jacket platform model is taken as research object. On the basis of the propagation properties of acoustic emission wave produced by crack formation and extension in jacket platform model, experiments on energy attenuation and acoustic emission testing are carried out, and the research on sensors'arrangement and auditory localization are conducted, too.The experiment that simulation acoustic emission source using broken lead on jacket platform model is carried out, the average real wave velocity is calculated, and the relationship between distance and signal amplitude is obtained. They provide the basis for determining the maximum distance between two sensors.Based on acoustic emission experimental study of one joint of jacket platform model, energy attenuation coefficient range from 0.30 to 1.70 is deduced. The attenuation coefficient is varying at the same distance from the sound source on different supports. This is because the actual structure medium is not entirely the elastic medium, and in the process of acoustic emission wave propagation, energy attenuation is affected by not only geometric attenuation, but also many other factors such as the shape and size of the structure. Experimental research also proves this point. According to the experimental conclusion, the sensors'arrangement method based on energy attenuation is put forward, the global testing of prototype structure which needs 22 sensors and the sensor arranging scheme are preliminary deduced. The study of acoustic emission sensors'arrangement is the key to conduct research on acoustic emission testing of offshore platform. In fact, we need to obtain useful data through the test, because the theoretical study of acoustic emission sensor arrangement which is closely related to such factors as the material and the size of the offshore platform are rare.Finally, according to the principle of acoustic emission source localization, the time difference line positioning method is used in the acoustic emission source simulation test which is experimented on a main leg of the offshore platform. Judging from the experimental results, the test error is within 7mm and the source position obtained with this method is quite reasonable. Therefore, the use of time difference line positioning method to determine the position of the single damage in one support of the offshore platform is feasible.Overall, the test results and analysis shows that the key factors influencing the precision of the auditory localization are acoustic emission wave attenuation and superposition. The localization method also has an important effect on determining the accurate acoustic emission source position. To improve the accuracy and reliability of auditory localization in the acoustic emission testing, acoustic emission sensors must be arranged reasonably to receive the real and effective waveform, acoustic emission testing experience based on understanding of the principle of localization method thoroughly should be accumulated, and corresponding effective measures which reduce the influence of main factors must be adopted.